Powertrain Controls - ECM/PCM

Code 21:

CTS Circuit:

CIRCUIT DESCRIPTION:

The throttle position sensor (TPS) provides a voltage signal that changes relative to throttle blade angle. Signal voltage will vary from about 0.4 at idle to about 5.0 volts at wide open throttle.

The TPS signal is one of the most important inputs used by the PCM for fuel control and for most of the PCM control outputs.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. Code 21 will set if:

^ TPS voltage is greater than 4.8 volts at any time.
^ Engine is running and air flow is less than 15 gm/sec.
^ TPS signal voltage is greater than 0.80 volt.
^ Code 34 not present.
^ All conditions met for 5.0 seconds.

NOTE: With closed throttle, ignition "ON," or at idle, voltage at "BB10" should be 0.33 -0.46 volt. If not, check adjustment.

2. When the TPS sensor is disconnected, the TPS voltage will go low and a code 22 will set. Therefore, the PCM and wiring are OK.

3. Probing CKT 452 with a test light checks the sensor ground CKT. A faulty sensor ground circuit will cause a code 21.

NOTE: If a code 21 is set, the PCM will not allow 4th gear or TCC operation.

DIAGNOSTIC AIDS:

The on-board diagnostics ED01 reads throttle position in volts. With closed throttle, ignition "ON" or at idle, voltage should be 0.33 -0.46 volt.

An open in CKT 452 will result in a code 15 and 21. Refer to "INTERMITTENTS" in DIAGNOSIS BY SYMPTOM.

Check For:

^ Poor Connection or Damaged Harness - Inspect PCM harness connectors for backed out terminal "BB10," improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

^ Intermittent Test - If connections and harness check OK, observe ED01, TPS voltage while moving related connectors and wiring harness. If the failure is induced, the display will change. This may help to isolate the location of the malfunction.

^ TPS Scaling - Observe ED01 TPS voltage while depressing accelerator pedal with engine stopped and ignition "ON." Display should vary from closed throttle TPS voltage (0.33-0.46 volt) when throttle was closed, to over (4.0 volts) 4000.0 mV when throttle is held at wide open throttle position. Typically, accelerator pedal travel only yields 4.1 or 4.2 volts maximum, but full throttle rotation at the throttle body should be about 5.1 volts.